(1) Field of the Invention
The present invention relates to a ceramics composition, particularly to a dielectric ceramics composition which has low temperature sintering properties to such an extent that Ag, Cu, or an alloy mainly containing Ag or Cu can be used as an internal conductor, and which has a low dielectric constant and a high linear expansion coefficient.
(2) Description of the Related Art
In recent years, thick film forming processes such as a printing process and a sheet process have been used to manufacture chip components such as a chip capacitor, a chip inductor and a chip filter. Moreover, examples of an electronic device formed by co-firing a plurality of types of ceramics compositions different in material properties include an LC filter formed of a combination of a magnetic material and a dielectric material, a circuit substrate (element) incorporating a capacitor formed of a combination of a high dielectric material and a low dielectric material, and the like.
For example, for the capacitor formed by co-firing the high and low dielectric materials, the reduction of distribution capacity, and the like can be performed, as compared with the capacitor formed only of the high dielectric material. Moreover, as compared with the capacitor formed only of the low dielectric material, the capacity enlargement can be realized.
In the above-described electronic device, in order to enhance the loss properties, it is preferable to use low-resistance Ag, Cu, or the alloy mainly containing Ag or Cu as a conductor electrode. However, since such conductor metal has a low melting point, it is requested that the ceramics composition for use in the electronic device can be sintered at the melting point of the conductor metal or a lower temperature (has a low temperature sinterability).
Moreover, to co-fire a plurality of types of ceramics compositions, the linear expansion coefficients of the respective ceramics compositions have to be matched to some degrees. When there is a large difference of linear expansion coefficient, the sintered product is cracked. For example, in general ceramics compositions provided with perovskite structures such as oxide titanium, barium titanate and calcium titanate, tungsten bronze structures such as barium-rare earth-titanium oxide, spinel structures such as NiCuZn-based ferrite, and the like, the linear expansion coefficient is of the order of 80xc3x9710xe2x88x927/xc2x0 C. to 130xc3x9710xe2x88x927/xc2x0 C. Even in the ceramics composition provided with the low temperature sinterability by addition of glass or the like, the linear expansion coefficient is substantially the same as the original linear expansion coefficient (about 80xc3x9710xe2x88x927/xc2x0 C. to 130xc3x9710xe2x88x927/xc2x0 C.) In many of the conventional low-dielectric ceramics compositions mainly containing glass, however, the linear expansion coefficient is in a range of about 40xc3x9710xe2x88x927/xc2x0 C. to 80xc3x9710xe2x88x927/xc2x0 C., the linear expansion coefficient is lower than that of the dielectric material or magnetic material provided with the low-temperature sinterability by the addition of glass or the like, and there is a problem that when the materials are co-fired, the product is cracked.
The present invention has been developed in consideration of the above-described situations, and an object thereof is to provide a low-dielectric ceramics composition which has a low-temperature sinterability and can be sintered with an internal conductor alone, and which has a high linear expansion coefficient and can be co-fired with other ceramics compositions.
To attain this object, according to the present invention, there is provided a ceramics composition which mainly comprises Ba-based glass and xcex1 quartz. The content of the Ba-based glass is in a range of 55.0 to 69.4 wt %, the content of the xcex1 quartz is in a range of 12.1 to 40.2 wt %, and the content of Al2O3 is 24.5 wt % or less. For the components of the Ba-based glass, in terms of oxides, the content of BaO is in a range of 19 to 29 mol %, the content of SiO2 is in a range of 62 to 72 mol %, the content of Al2O3 is in a range of 6 to 11 mol %, and the content of B2O3 per the total of 100 mol of BaO, SiO2 and Al2O3 is in a range of 3 to 7 mol.
Moreover, in the ceramics composition of the present invention, the linear expansion coefficient is in a range of 80xc3x9710xe2x88x927/xc2x0 C. to 150xc3x9710xe2x88x927/xc2x0 C.
Furthermore, the ceramics composition of the present invention comprises the xcex1 quartz, and one of four types of crystal phases [BaAl2SiO8+BaSi2O5], [BaAl2SiO8+BaSi2O5+Al2O3], [BaAl2SiO8+Al2O3] and [BaSi2O5+Al2O3].
In the present invention, the sintering temperature of the ceramics composition is equal to or less than the melting point of Ag, Cu, or the alloy mainly containing Ag or Cu, and the dielectric constant is low, but the linear expansion coefficient is high. Therefore, the co-firing can be performed with different types of ceramics compositions such as the high dielectric material and magnetic material which can be sintered at a low temperature. By using low-melting metals such as Ag and Cu as the internal conductor, the composition can be used for manufacturing electronic devices such as a small-sized filter, a resonator and a circuit substrate.